Resistance unit



Dec. 8,1931.

AN d

S. B. ALLEN RESISTANCE UNIT Filed March 50, 1928 fig. z.

Live; No i* 11a fo r'd/ l?. dlezz M KM d lo z *n g? Patented Dec. 8, 1931 STRATFORD B. ALLEN, F CAMBRIDGE, MASSACHUSETTS RESISTANCE UNIT Application filed March 30, 1928. Serial No. 265,885.

This invention relates to improvements in resistance units and processes for their manufacture. More especially it relates to the terminal capping of tubular units.

4The tube may for example be of glass, with a metal lying dispersed in extremely small particles over the interior surface of the tube. This provides a non-inductive resistance, which has been found particularly useful in connection with radio apparatus in the range between 200 ohms and l5 million ohms, but which is also capable of being made for low resistance.

The invention provides improvements rel,

lating especially to the closing of the tube ends by metallic caps, and to the connections of the caps, interior and exterior, mechanical and electrical. It provides a method of manufacture simpler and cheaper than heretofore; and a product correspondingly less expensive. It improves the uniformity and reliability of mass production of such units; also it makes them more rugged and dependable in service. An important feature contributing to these results is the elimination of delicate operations heretofore requisite, with substantial saving in material and labor. Further it provides for the speedy making of the permanent connections when a com-- pleted unit is put into service; and provides especially for the setting of a series of umts branching from a single conductor, without certain costs for preparation, installation and connection that attend the use of all other units of this nature heretofore known to me, including a considerable saving in labor costs in the industrial use of such a unit.

The terminal caps hitherto used are metallic cups which fit over the ends of the glass tube. The cap of the invention has a central interior mound leaving an annular groove into which the annular wall constituting the tube can be received. A relatively small quantity of hot molten sealing alloy having been deposited in the groove, and the up end of the tube being closed, temporarily or permanently, and the usual plug or stopper being omitted from thelower end of the tube, the lower end of the tube is" to be thrust down io into the said molten alloy in the groove.

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Heating and expansion of entrapped air results, and this drives some of the alloy out from the tube interior by forcing it up between t-he tube and the surrounding wall of the cup. The glass becomes heated from both inside and outside so that the glass does not break from heat stresses. The liquid alloy behaves peculiarly. Even though it be a substance which does not wet the glass, but which when in contact therewith initially and normally assumes a convex surface formation toward the glass surface, it in the circumstances stated can be made to assume a concave surface curve extending up the tubes interior, like a concave meniscus. I be- Clieve this phenomenon due to the combined effect of the said expulsion of air and of the cooling and solidification of liquid which occur where it contacts with the glass, the former continuing after the latter has begun. Having solidified, this alloy provides the necessary mechanical security of position and electrical interior connection of cap with resistance. Exteriorly, the cylindrical sides and protuberant terminal cone of the cap adapt the unit for convenient connections according to practice heretofore; but there is added a groove crossing the axis of the protuberant cone, of proper size to receive a conductor wire and, with a bit of solder to hold it in permanent security. It is a feature that the terminal grooves at the two ends of a unit may be in a plane together, or may be arranged at angles to each other, so as to connect wires running in different directions, and that this angular arrangement can be made very inexpensively.

It is intended that the patent shall cover by suitable expression in the appended claims, whatever features of patentable novelty exist in the invention disclosed.

In the accompanying drawings: Figure l is an elevation of a resistance unit embodying the invention, with terminal grooves in the same plane; Y

Figure 2 is an elevation, in medial section y on line 2-2 of Figure l on a larger scale;

Figure 8 is an elevation showing a group ofthe units, illustrating terminal slots in a unit arranged angularly with respect to each other; and

" .Figure liis a plan of the same.

Referrin to the drawings, a tube or shell vrepresente in this instance as being ot glass,

Ais to be capped at each end by. metallic cups 12. Such may be inexpensively formed from solid rod stock by automatic machinery.

Prior to the assembling of the unit the shell willhave been treated interiorly so as to constitute a conductor having the desired resist- .the tube,

ance. For this the drawings represent at 14 1 a thin deposit; but the substance thus deconducting material.

An important feature resides in the inex- 'pensive method by which permanent electrical contactl is attained betweenthe interior high resistance surface of the lsliell and the end caps 12, and at the same time the caps become secured rigidly and permanently on the endsof the shell. For these purposes each cap, instead of having the usual concave conical bottom left by the drill which excavated its interior, has interiorly a central mound 16 of unexcavated material between which moundand thecylindrical wall of the cap lies an annular tube-receiving valley or groove 18. When a unit is to be assembled a little molten sealing alloy 19 is placed in the cup 12, which is then held with its axis vertical so that the liquid 19 distributes itself throughout the groove 18. Preferably an falloy isused having characteristics of similarity to type metals. This melts ata high temperatureascomparedwithordinarysolder. The workman, closing the upper end of the tube 1'0 with his finger (protected by a rubber glove), but leaving the lower end of tube open, inserts the lower end of the tube into thev said groove in the cap. Air is thus en-l trapped in the tube between linger and cup, becomes highly heated by the molten alloy, and thus 'acquires expansive pressure sufficient to prevent the liquid from rising freely within the tube, as the end of tube sinks into the liquid, and t0 cause some of the liquid alloy to be forced out between the outside wall of the tube and the closely surrounding barrel 12 of the cup, passing out through 1rregularities which always exist in the bottom edge'of the glass tube 10. Assuming that the molten alloy was notsupplied to the cup in such quantity as is illustrated iii the top part of Figiure 2, suiicient to overflow the central moun nor in such quantity that the insertion of the tube raises its level to this extent,

poses the glass that is, assuming the condition portrayed in the bottom part of Figure 2, the expulsive elect on the liquid is enhanced by the fact that the only surface which can yield to the expanding airis the surface of liquid near the wall of thetube. For a given expansion of air the'liquid is therefore depressed to u, greater distance than if itlay across the entire bottom of the cap. As the soliditication next to the cool body of glass and next to the cool body of the central mound, the expulsion occurs to a greater extent-from the middle space of the groove. The'metal which is forced out may be recovere and used again. Such as remainsbetween the walls of the tube and cup as at 20 solidifies there and assures a tight lit. That which remains within the. tube lies in the bottom of the groove and has a surface 20 like a concave meniscus reaching from the interior mound 16 of the cup 'to the coated tube wall. Because of the presence of the unexcavated material 16, and because of the quasi-meniscus formation 2() the quantity of sealing alloy 19 consumed in making certain 'a good electrical and mechanical joint is far less than heretofore required to fasten a cap on a tube. Also there is less dimension of space from contraction, if contraction occurs in cooling. The leaving of the end portion ofthe interior of the tube open for the heat reaction between air and alloy, by omitting the cork plug heretofore used, both saves the cost of making and inserting the plug, andalso exto a temperature at its inner face approximating that to which its outer face is subjected, thus preventing glass breakage from unequal heat stresses. l

One end of the shell having been capped, the other end may be capped in like manner; and a complete, simple, substantial and eiicient resistor unit results.

If it happens that more seallng alloy than necessary is run into the groove, for example, enough to cover the central mound as is represented to have happened when the end at the top of Figure 2 was sealed, the resulting product may nevertheless have the predetermined desired resistance value, approximately. Before the sealing a band of carbon may be laid over the resistance substance at each end of the shell as indicated at 22, to a width suitable to leave a predetermined length ofthe resistance between bands. This may be done by preliminarily dipping the coated tube end into a liquid having carbon in suspension, as a paste of ground graphite, and then letting it dry; or by otherwise painting the interior with carbon or other conductor with which the alloy will readily connect. The electrical resistance of the unit will then be substantially that of the higher resistance deposit lying between the carbon bands, `and a variation in height of sealing alloy will n'ot appreciably vary the total resistance.v

Exterior conical points 24 on each end cap 12 constitute the terminals of the unit and are adapted to fit the ordinary spring clips (not shown) which are sometimes available for mounting such units between conical sockets; or the barrel walls 12 of the cap may be set into ordinary cylindrical clamps. AAccording to the invention, however, additional means is provided for effecting permanent connection of a unit in an electricalV circuit. A groove 26, cut acro'ss the exterior of each cap in the plane of the axis, is adapted to receivea Wire 28er 30 crossing the axis lengthwise of the groove, where a drop of solder will secure it quickly and permanently. An important feature is that the grooves in opposlte terminals of a particular unit may be arranged at any desired predetermined angle with respect to b each other. Then in a series of units, indicated in Figure 3 of the drawings, a single bare wire conductor 28 may run in a straight line through' one terminal of every unit of the series; and the several opposite terminals, at the top of Figure 3, may be connected to individual conductors 30 extending in various directions, which is an important element of structure, especially in cases where it is desired to organize the units close together on a very short length of wire 28. The making of the desired angles of groove direction can be accomplished withl precision by the .setting of automatic machinery cutting the groove, if this be done after the caps have been fixed rigidly on the tube. Or, if the grooves are cut before assembly, it is only a matter of setting the cap with its groove at the angle desired, when aiixing the second cap. The invention makes it possible for the unit to be set up on wires 28, 30 with ordinary solder such as the public are accustomed to use. This is made ssible by the use of a sealing alloy 19 within,

, `whose melting point is higher than that of l ordinary wire solder, such as half lead and half tin; and this in by the described method which prevents the glass from undergoing heat strains due to'V unequal a plication of high temperatures. The intro uction of such a high melting allty alsopermits of the subsequent operating he resistance at higher load than resistances of this type heretofore made by others, because the increase of temperature resulting from the higher load does not melt this alloy as it might the Woods metal or like alloy heretofore commonly used for interior sealing because its low melting point is safer for glass. The presence of the carbon band tends to prevent the alloying of the` sealing alloy with the metal that is in position on the interior of the tube to constitute the resistance. The composition selected for the rnal conductor in the turn is made possible.,

sealing alloy is preferably one which has as near as may be the same coeiiicient of expansion as the glass, in order not to shrink awa from it in cooling, and in order not to break it by expansion. v

The completed product disclosed has many advantages, among which are the' ease and simplicity of making perfect and permanent connection of a series of the units in electrical apparatus; the small amount of solder needed; the ability to use ordinary solder to ensure proper connection of exterterminal groove; and the high temperature at which the unit can be operated. `Advantages in its manufacture are the smallness of the labor cost in assembling the unit; the saving in work and in quantityl of sealing alloy by n-ot removing the central interior mound when the cap is made; the further saving of sealing alloy y reason of the quasi-meniscus surface edges; and the saving of labor and the cost of plug and of glass breakage heretofore experienced. Another feature is the um'- formity of product obtainable by the process, as regards approximation of the unit to the standard value predetermined for it; and another the mechanical strength with which the sealing alloy, rising within the glass and forced up outside of it Within the barrel of the cap, holds the glass in the cap.

I claim as my invention:

1. A resistance unit comprising an insulating tube with interiorly coated resistance in tubular form; a terminal, fitting over an end of the tube, with internal control mound; and a sealing medium connecting said mound to said interiorly coated resistance.

2. A resistance unit comprising an insulating tube with interiorly coated resistance; a metallic cap with internalk mound and with internal annular groove around the mound adapted to receive an end of said tube; and means within said groove connecting said cap electrically tov said' interiorly coated resistance with incidental mechanical connection of it to the tube.

3. A resistance unit comprising an insulating tube with interiorly coated resistance; a. metallic cap into which an end of said tube is set; and an alloy within the cap, solidified with an annular concave surface extending between the interior surfaces of tube and cap, connecting the tube and cap mechanically and electrically.

4. A resistance unit comprising an insulating tube with interiorly coated resistance; an interior terminal therefor, comprising a. band coating the end of the inner surface of thet'ube, of greater conductivity than other portions of said inner surface; a metallic cap into which the end of said tube with band is set; and an alloy Within the cap, solidified with a concave surface rising over the said ing said mound annularly with the band, connectin the tube and cap mechanically and electmcally.

5. A resistance unit comprisingV an msulating tube with interiorly coated resistance; a metallic terminal cap, with internal mound, for the end of the tube; and an alloy connectinterior of the tube mechanically and electrically, part of said alloy being within and adheringl to the end portion of the tube; and the said alloy being of a variety whose melting point is of an order above that of the order of alloys comprising approximately half lead and half tin. y

6. A resistance unit comprising an insulating tube with interiorly coated resistance; a metallic cap, with internal annular groove adapted to receive an end of said tube so that an annular wall of the cap is outside and al central mound' of the cap is inside said tube; and an alloy solidified with a concave surface rising annularly over the inner surface of the tube, connecting the tube and cap mechanil cally arid electrically.

7. A resistance unit`F comprising an insulating tube with interiorly coated resistance; metallic terminal caps for the ends of the tube, each cap having'a portion enclosing andl a portion enclosed by the `end part of the tube and a body of solid conducting material at -the end part of the tube extending thence t0 said enclosing and enclosed parts of the cap, filling the annular space between cap and tube, and connecting the cap mechanically and electrically to the tube.

8. A resistance unit comprising an insulating tube with interiorly coated resistance, and a terminal cap xedly connected therewith, having for exterior connection a portion which is fixed relative to the tube and is grooved transversely of the axis of said unit.

9. A resistance unit comprising an insulating tube with interiorly coated resistancev having terminal caps, each with exterior portion grooved transversely of the axis of said unit for exterior connection, the grooves at the two ends being set at an angle with respect to each other about the axis.

Signed at Boston, Massachusetts, this fourteenth day of January, 1928.

, 0STRATFORD B. ALLEN. 

